Switching circuit for measuring the electrical power in two energy flow directions (delivered and returned)

ABSTRACT

An electronic counter for measuring the electrical power in two energy flow directions (delivered and returned) is disclosed. The circuit comprises an integrator for the product of current and voltage, and a first pair of threshold circuits having a predetermined positive voltage threshold circuit and a predetermined negative voltage threshold circuit connected at their outputs to a bistable flip flop circuit. A second pair of threshold circuits, whose two predetermined threshold levels are higher than the threshold levels of the first pair of threshold circuits, is connected in parallel with the first pair of threshold circuits. An additional flip flop circuit is connected after this second threshold circuit. The outputs of the two flip flop circuits are connected via an exclusive OR circuit to the input of the integrator to change the polarity of the input signal in response to changes in direction of the power flow. Two counters are connected through a gate circuit to the outputs of the flip flop circuits to count signals proportional to the power and to feed the signal to one counter for energy flow in one direction and to the second counter for energy flow in the opposite direction.

United States Patent 1 Schwendtner [54] SWITCHING CIRCUET FOR MEASURINGTHE ELECTRICAL POWER IN TWO ENERGY FLOW DIRECTHQNS (DELIVERED ANDRETURNED) [75] Inventor: Manfred Schwendtner, Schwarzenbruck, Germany[73] Assignee: Siemens Aktiengesellschaft, Munich,

Germany [22] Filed: June 12, 1972 [21] Appl. No.: 261,657

[30] Foreign Application Priority Data June 11,1971 Germany ..P 21 28833.5

[51] Int. Cl. ..G0lr 21/00 [58] Field of Search ..324/142 [56]References Cited UNITED STATES PATENTS 3,470,471 9/1969 Moore ..324/1423,510,772 5/1970 Luthi ..324/142 H -Uol 0 Primary Examiner-Alfred E.Smith Attorney-Hugh A. Chapin 5 7 ABSTRACT An electronic counter formeasuring the electrical power in two energy flow directions (deliveredand returned) is disclosed. The circuit comprises an integrator for theproduct of current and voltage, and a first pair of threshold circuitshaving a predetermined positive voltage threshold circuit and apredetermined negative voltage threshold circuit connected at theiroutputs to a bistable flip flop circuit. A second pair of thresholdcircuits, whose two predetermined threshold levels are higher than thethreshold levels of the first pair of threshold circuits, is connectedin parallel with the first pair of threshold circuits. An additionalflip flop circuit is connected after this second threshold circuit. Theoutputs of the two flip flop circuits are connected via an exclusive ORcircuit to the input of the integrator to change the polarity of theinput signal in response to changes in direction of the power flow. Twocounters are connected through a gate circuit to the outputs of the flipflop circuits to count signals proportional to the power and to feed thesignal to one counter for energy flow in one direction and to the secondcounter for energy flow in the opposite direction.

3 Claims; 7 Drawing Figures 5 PAIENTE MM 1191a sum 1 m 2 Fig. 3

ELECTRICAL POWER IN TWO ENERGY FLOW DIRECTIONS (DELIVERED AND RETURNED)BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to a circuit for measuring the electrical power in two energyflow directions (Delivered and Returned), comprising an electronic kWhmeter which converts the output of a multiplier, which is the product ofcurrent and voltage, into a pulse sequence of the same valence. This isaccomplished by means of an integrator and two threshold stagesconnected behind the integrator, as well as a bistable flip flop stagewhich upon attaining a time integral corresponding to the pulse value,reverses the polarity of the integrator input quantity.

2. Description of the Prior Art At large transfer points between variouselectric power-supply stations the direction of the electrical powerflow may change. It is necessary, therefore, to measure and indicate thepower separately according to whether the flow of the power is in thedirection of power delivered or power returned. the kWh meterspreviously used at these locations measured the energy quantities withthe desired accuracy in only one direction. As a result, one is forcedto employ two such precision instruments.

An electrical meter is presently known which can be utilized to measurepower flow in both directions. In order to cancel the error in the meterin the opposite direction of rotation to that being measured, a deviceis provided that depends on the sense of rotation of the meter armatureand switches on a compensation means to compensate the error occurringduring the return movement of the armature. The additional compensationdevices which are necessary for this purpose entail not only greaterexpenditure and greater space requirements, but are also difficult toadjust.

Another counter for dual power flow directions is also shown in GermanPat. No. 1,516,966 wherein a device, which depending on the direction ofthe power or energy flow, produces a switch in the meter voltage, orcurrent, path, reverses the voltage or current pulses of the meter whenthe direction of the energy flow is reversed and changes to a two-ratemeter mechanism. Because this device depends on the energy flowdirection or the rotational direction discriminator, each time the senseof rotation of the counter is reversed, following a change in thedirection of energy, that is, when the counter wants to run backward,the voltage or current path will be switched so that the counter willmove forward, in each energy direction.

SUMMARY OF THE INVENTION It is an object of the invention to provide aswitching circuit for measuring power in two energy flow directions,comprising an electronic kWh meter previously described in detail.According to the invention, the switching circuit features two thresholdstages connected to the output of the integrator. and two flip flopstages connected to the output of each threshold stage with the outputsignals of both flip flop stages connected, on one hand, to the inputsof an exclusive OR circuit whose output signals produce polarityreversal at the input to the integrator, and, on the other hand,

the output signals of both flip flop stages are connected, by gatecircuits, to one meter mechanism, one connection for Return and one forDelivery. In this manner, the coordination between the output signal ofthe bistable flip flop stages and the polarity at the input of theintegrator is inter-changed so that the same meter can measure thedelivered as well as the returned energy, with the desired accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is shown in thefollowing detailed description with reference to the drawings, showing aschematic illustration of an exemplary embodiment in which:

FIG. 1 is a basic circuit diagram of an electronic kWh meter for bothenergy flow directions.

FIG. 2 is the time curve of the output voltage of the integrator duringenergy flow in one direction.

FIG. 3 is the time curve of the output voltage of the integrator duringa change of direction in the energy flow, without the additional deviceof the invention.

FIG. 4 is the time curve of the output voltage of the integrator duringa change in direction of the energy flow, when the circuit according tothis invention is present.

FIG. 5 is the time curve of the output voltage of the integrator withoutenergy flow in the presence of zero errors and drifts.

FIG. 6 is the time curve of the output voltage of the integrator, aswell as of the voltage and the signals at the various stages, duringerror compensation, employing the circuit constructed according to theinvention.

FIG. 7 is an illustration of various threshold voltages to which thethreshold switches respond.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. I the actual multiplieris not shown but is represented symbolically by two voltage sources +U,,and U,, which deliver voltages +U,, and -U Normally, voltage U isproportional to the measurement of the effective power delivered bypower-measuring transducers. Through contacts S and S of relay S,voltages +U,, and -U,, are connected by a resistor R to an integrator Jat the output of which a voltage U,, appears. This voltage U is appliedto the thresholdtrigger stages T1 and T2 which are connected with abistable flip flop stage M1, the output of which is connected throughrelay S, to the input of the integrator J. Thus, the voltage U,alternates positively and negatively, depending on the polarity andvalue of voltage U, appearing at the output of the integrator J. VoltageI], has a curve as shown in FIG. 2. If, for example, U,, is connected tothe input of the integrator J and if voltage U reaches the value Uthreshold stage Tl responds and causes flip flop stage M1 to assume theopposite state. A switch connects the relay S to the voltage output offlip flop Ml so that voltage +U,, is now connected to the input of theintegrator J as illustrated in FIG. I. This condition remains until thecurve of voltage U reaches value U At this point the threshold stage T2responds and returns the flip flop stage M1 to its original position.Relay S thereby changes and the integrator J again receives voltagevalue U,, through contact S Also connected to the output of the bistableflip flop stage M1, is a counter mechanism ZWl which counts one unitwhen the bistable flip flop stage Ml flips from position D (i.e., powerdelivered) into position R (i.e., power returned). The bistable flipflop stage M 1 is a so-called R-S flip flop; it alters its initialstate, therefore, only if it receives an input from the second inputafter having been set by the first input. Input R of the bistable flipflop stage M1 is provided with threshold stage T1 and input S isprovided with threshold stage T2. Threshold stage Tl responds at voltageU and threshold stage T2 responds at voltage U Hence, a repeated pulsetransmission by threshold stages T1 or T2 does not change the state ofthe bista ble flip flop stage M1 unless the other stage has responded inthe interim.

FIG. 2 shows the curve of the output voltage of the integrator when theflow of energy proceeds in one direction.

FIG. 3 shows the behavior of the described circuit if the energy flowdirection has changed at time point 1 At the time t,, threshold stage T2has responded and the bistable flip flop stage M1 has assumed acondition such that AU,,/At 0. At the time 2 the polarity of U might nowchange so that AU /At 0. At the time the threshold stage T2 againresponds. However, as required, the bistable flip flop stage M1 does notchange its switching position, so that relay S is not activated. VoltageU continues to rise above the value U up to saturation voltage -U, ofthe integrator J. At this point, the entire switching arrangement isblocked. This state occurs when the voltage U,,which is designed to beproportional to the effective power, to be measured-changes itspolarity, through power reversal at the measuring point, e.g., atransfer point. This blockage of the switching circuit is desired if theenergy flow is only to be measured in one direction. It prevents the kWhmeter from running under idle conditions.

The present invention is based on the concept of determining anapproaching blockage in time, and to perform the switching operation insuch a way that the blockage will be arrested and, if the conditionwhich originally led to the blockage continues, the counting pulseswhich correspond to the quantity of energy to be measured, will bedelivered to a second counting mechanism ZW2.'Thus, the changes in theposition of the bistable flip flop stage M1, from D to R" are determinedand utilized as counting pulses.

To this end two more threshold stages T3 and T4 and another flip flopstage M2 are provided. Furthermore, an exclusive OR circuit A isemployed. The mode of operation is illustrated in FIGS. 1 and 4. In FIG.4, the following relations apply: U U and U U The followingdeterminations apply when U 0: The D signal at the output of the flipflop stage Ml connects +U,,, through switch contact 8,, to the input ofthe integrator J. An R signal at the output of the flip flop stage Mlconnects the voltage -U,,, through.

/ At 0, due to the signal inversion through the in-- tegrator J. At timepoint voltage U, 0, because ofa reversal in the direction of the energyflow. Because nothing changes in the condition of relay S, AU A! 0. Atthe time t the threshold stage T2 responds again; but the output signalfrom flip flop stage M1 does not change. When the voltage U, howeverreaches the value U threshold stage T4 responds setting flip flop stageM2 to the D condition. Because a fil, when stage M2 is in the Dcondition, the coordination between the flip flop stage M1 and the relayS interchanges, which means that the circuit to contact S is opened andthe circuit to switch contact S is closed. Since it is a prerequisitethat U, 0, and +U 0, AU [At now becomes AU At 0.

As soon as threshold stage T4 has responded (m2 D), the counting pulsestransmitted from flip flop stage M l are guided through gate circuit N,to counting mechanism ZW2. Thus, while counting mechanism ZWl registers,for example, the return energy, counting mechanism ZW2 registers thedelivered energy.

As seen in FIG. 1, the switching arrangement of the present inventioncomprises two more circuit members B1 and B2, which are illustrated inform of relays and are excited by the outputs of the threshold stages T3and T4. With the aid of these circuit members B1 and B2, a positive or anegative compensation voltage +U or U,, can be applied to the input ofthe integrator, through a resistance R, and may produce a correspondingcompensation current J The mode of operation is described in greaterdetail in FIGS. 5 and 6. 1

Error voltages and currents occur in all real integrators. They lead tochanges in the output voltage U of the integrator J even when the inputvoltage U, at the input of the integrator equals zero. Since themagnitude of integrator error with respect to its direction andmagnitude does not depend on the position of switch S the followingapplies according to FIG. 5: At time t it should be m2 R and the voltageU, 0. Due, however, to the magnitude of the error, theoutput voltage U,of the integrator J changes slowly. At time t the threshold voltage ofthe threshold stage T1 is reached. Therefore, nothing changes in thecurve of the voltage. At time threshold stage T3 responds and switchesthe counter mechanism 2W2 to the other energy direction, through'a flipflop stage M2 and the exclusive OR circuit A. Voltage U continues torise until the saturation voltage +U, of the integrator J is attained.

Assuming that at the time t the switch position was on return, aswitch-over would be effected to delivery at the time 1,. Now, if attime t the voltage U deviates from zero, namely, to a polaritycorresponding to the 7 energy in .the return direction, the outputvoltage U will not change, because-due to the error magnitude of theintegratorthe Delivery" switching position prevails, which means,however, that the kWh meter is blocked. This state is prevented byswitches B1 and B2 which are actuated by threshold stages T3 and T4. As

. soon as either the threshold stage T3 or the threshold 4 in FIG. 6.

In FIG. 6 the first diagram shows the curve of the output voltage of theintegrator U the second diagram shows the time curve of the inputvoltage U, to the integrator, the third diagram shows the switchingposition of the flip flop stage M2, the fourth diagram shows thedependency of the compensation current and the last diagram shows theswitching position of the flip flop stage M1.

At the time t,, the threshold stage T3 responds. As a result, the outputm2 conducts a D signal which corresponds to Delivery. At the same time,a compensation current +J is connected, through switching stage B1, tothe input of the integrator J until the output voltage U, of theintegrator decreases by the amount AU which is the hysteresis voltage ofthe threshold stage T3. Thereafter, the compensation current is switchedoff and the output voltage U of the integrator rises again, untilvoltage U is reached. The threshold stage T3 responds and sets the flipflop stage M2, so that output m conducts an R signal, meaning it isswitched to Return. This is continued many times.

At time t,, the output m of flip flop stage M2 is set to D signal whichis established as meaning Delivery." At the same time, the return ofenergy may occur so that the input voltage U, of the integrator Jassumes the incoming polarity. Due to the signal inversion by theintegrator J, the output voltage U now rises quickly up to voltage Uwhich switches, by threshold stage T3, the output m of the flip flopstage M2, to R, which means that at the time 2 the device is againswitched to Return. From this moment on, the counting pulses whichcorrespond to the quantity of energy are guided to the correct countingmechanism ZWl Return.

Thus, in the switching arrangement of the present invention componentranges are formed with threshold voltages U to U with the aid ofthreshold stages T1 to T4, for the range of the output voltage U of theintegrator J, as illustrated in FIG. 7. In place of relays S, B1 and B2,contact-free circuit members preferably are used.

In the foregoing, the invention has been described in reference tospecific exemplary embodiments. lt will be evident, however, thatvariations and modifications, as well as the substitution of equivalentconstructions and arrangements for those shown for illustration, may bemade without departing from the broader scope and spirit of theinvention as set forth in the appended claims. The specification anddrawings are accordingly to be regarded in. an illustrative rather thanin a restrictive sense.

What is claimed is:

l. A switching circuit for measuring electrical power in two energy flowdirections comprising an integrator means to obtain the integral of theproduct of the current and voltage formed by a multiplier,

a first pair of threshold circuits connected to the output of theintegrator means, one of the threshold circuits having a predeterminedpositive voltage threshold and the other threshold circuit having apredetermined negative voltage threshold,

at bistable flip flop circuit connected to the output of the thresholdcircuits,

a second pair of threshold circuits connected to the output of theintegrator means, one of the threshold circuits having a predeterminedpositive voltage threshold greater than the ositive voltage thres e oldof the first positive thres old circuit, t other of the thresholdcircuits having a predetermined negative voltage threshold greater thanthe negative threshold voltage of the first negative threshold circuit,

a second flip flop circuit connected to the output of the thresholdcircuits,

an exclusive OR circuit connected to the output of both of the flip flopcircuits, the output of the OR circuit being connected to the input ofthe integrator means to reverse the polarity of the input signal to theintegrator when the direction of the energy flow changes,

a gate circuit connected to the output of the flip flop circuits, and

a first and a second counter connected to the output of the gatecircuit, the first counter receiving an input from the gate circuit forpower flow in one direction, and the second counter receiving the signalfor power energy flow in the opposite direction.

2. A switching circuit for measuring electrical power in two energy flowdirections as set forth in claim 1 further comprising a compensationcircuit connected to the output of the second pair of threshold circuitsfor feeding a compensation current to the input of the integrator meansto overcome the error signals of the integrator.

3. A switching circuit for measuring electrical power in two energy flowdirections as set forth in claim 2 wherein the maximum compensationcurrent is substantially equal to the maximum input voltage divided bythe input resistance of the integrator means.

1. A switching circuit for measuring electrical power in two energy flowdirections comprising an integrator means to obtain the integral of theproduct of the current and voltage formed by a multiplier, a first pairof threshold circuits connected to the output of the integrator means,one of the threshold circuits having a predetermined positive voltagethreshold and the other threshold circuit having a predeterminednegative voltage threshold, a bistable flip flop circuit connected tothe output of the threshold circuits, a second pair of thresholdcircuits connected to the output of the integrator means, one of thethreshold circuits having a predetermined positive voltage thresholdgreater than the positive voltage threshold of the first positivethreshold circuit, the other of the threshold circuits having apredeterminEd negative voltage threshold greater than the negativethreshold voltage of the first negative threshold circuit, a second flipflop circuit connected to the output of the threshold circuits, anexclusive OR circuit connected to the output of both of the flip flopcircuits, the output of the OR circuit being connected to the input ofthe integrator means to reverse the polarity of the input signal to theintegrator when the direction of the energy flow changes, a gate circuitconnected to the output of the flip flop circuits, and a first and asecond counter connected to the output of the gate circuit, the firstcounter receiving an input from the gate circuit for power flow in onedirection, and the second counter receiving the signal for power energyflow in the opposite direction.
 2. A switching circuit for measuringelectrical power in two energy flow directions as set forth in claim 1further comprising a compensation circuit connected to the output of thesecond pair of threshold circuits for feeding a compensation current tothe input of the integrator means to overcome the error signals of theintegrator.
 3. A switching circuit for measuring electrical power in twoenergy flow directions as set forth in claim 2 wherein the maximumcompensation current is substantially equal to the maximum input voltagedivided by the input resistance of the integrator means.